We all have experienced how odors conjure strong emotional responses and memory associations, perhaps when encountering the familiar odor of a home after a long absence. In other animals, the links between odor, emotion and learning are stronger still. Therefore, the olfactory system is relevant to human experiences and as a model system to study the links between biological processes such as sensation, behavior, learning and emotion. Neuronal circuits within primary olfactory cortex are believed to mediate olfactory perception, learning and association. Yet important details of how different classes of neurons interact to form these circuits are at present poorly understood. We propose to study the function, in vivo, of a major group of inhibitory neurons that express the marker gene somatostatin (SOM), in order to better understand how the neuronal activity of olfactory cortex is regulated. To accomplish this we will virally introduce opsin proteins into olfactory cortex that enable the activity of SOM cells to be manipulated with light. By combining these manipulations with in vivo recording techniques we will determine the impact of SOM cells on neuronal activity and odor responses of olfactory cortex. Ultimately, these studies will improve our knowledge of how inhibition regulates those cortical neurons responsible for encoding odors and mediating odor learning.